1. Field of the Invention
The invention relates to a field effect transistor.
2. Description of Related Art
A field effect transistor may commonly include a channel region, an electrically conductive region, and a control region. The electrically conductive regions adjoin the channel and the control region is separated from the channel region by a transistor dielectric that adjoins the channel region.
The channel region is usually formed of a semiconductor material, for example a material whose resistivity lies between the resistivity of metals and the resistivity of insulators. Accordingly, the semiconductor material may have resistivity values of between approximately 10−4 and 10+12 Ωcm. Moreover, the channel region may commonly be formed of a monocrystalline material to provide good switching properties, such as low leakage currents when the transistor is in the off state.
The channel connection regions are commonly referred to as a source and a drain, respectively, and provide a connection to the channel region with the lowest possible resistance. The channel connection regions may contain highly doped semiconductor material and the resistivity of the semiconductor material is reduced by orders of magnitude due to the doping.
The transistor dielectric may be formed from insulating materials, such as silicon dioxide or materials having dielectric constant is considerably greater than the dielectric constant of silicon dioxide. The control region may be referred to as the gate. The control region may commonly be fabricated from a metal or from polycrystalline silicon.
Field effect transistors can be classified into planar field effect transistors and vertical field effect transistors. In the case of planar field effect transistors, the channel region is formed parallel to a substrate surface that may contain the active regions of multiple electronic semiconductor components. In the case of vertical field effect transistors, the channel region is formed transversely and in particular perpendicular to the substrate surface. The current flow in the channel region may be either perpendicular to the substrate surface or parallel to the substrate surface. In the case of a monocrystalline channel region, a control region that is made of a polycrystalline semiconductor material or made of a metal has been considered sufficient since only a control voltage is commonly applied via the control region. Therefore, the current flow with regard to the control region is considered only secondary. This approach leads to restrictions in the design of the integrated circuit arrangement.
These disadvantages become even more evident in the case of field effect transistors for memory cells. Memory units that effect volatile storage and have multiple memory cells include vertical field effect transistors arranged in trenches for connection with capacitors. Problems from the customary approaches arise in regard to leakage associated with the connection regions buried in the trench (buried straps), the production steps for connection regions buried in the trench (buried straps), the space requirement in the arrangement of adjacent transistors, and floating body effects.
Accordingly, there is a need for a field effect transistor that is constructed in a simple manner and is simple to produce. Further, such a field effect transistor may enable the simple production of integrated memory cells and other integrated circuits.